Semi-automatic and/or fully automatic firearms, such as rifles and shotguns, are designed to fire a round of ammunition, such as a cartridge or shotshell, in response to each squeeze of the trigger of the firearm, and thereafter automatically load the next shell or cartridge from the firearm magazine into the chamber of the firearm. During firing, the primer of the round of ammunition ignites the propellant (powder) inside the round, producing an expanding column of high pressure gases within the chamber and barrel of the firearm. The force of this expanding gas propels the bullet/shot of the cartridge or shell down the barrel.
Conventional firearms may have an integral upper receiver and hand guard. The removable hand guard section can be fastened to the upper receiver with screws or other similar fasteners. Conventional firearms having an upper receiver with integral hand guard may impede field removal and replacement of the barrel. In an M4 type firearm having an upper receiver with integral hand guard, the barrel nut may be covered by the hand guard limiting accessibility to the barrel nut.